首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1558356篇
  免费   24665篇
  国内免费   7031篇
电工技术   34527篇
综合类   6421篇
化学工业   272833篇
金属工艺   65047篇
机械仪表   43727篇
建筑科学   47111篇
矿业工程   11440篇
能源动力   50448篇
轻工业   118957篇
水利工程   15572篇
石油天然气   37673篇
武器工业   132篇
无线电   197796篇
一般工业技术   292604篇
冶金工业   190266篇
原子能技术   34071篇
自动化技术   171427篇
  2021年   15655篇
  2020年   11923篇
  2019年   14704篇
  2018年   16392篇
  2017年   15766篇
  2016年   21713篇
  2015年   17426篇
  2014年   28794篇
  2013年   88146篇
  2012年   36560篇
  2011年   49557篇
  2010年   43246篇
  2009年   51424篇
  2008年   46123篇
  2007年   43429篇
  2006年   45565篇
  2005年   40247篇
  2004年   42450篇
  2003年   42289篇
  2002年   41190篇
  2001年   38453篇
  2000年   36776篇
  1999年   36353篇
  1998年   53519篇
  1997年   44228篇
  1996年   38725篇
  1995年   32780篇
  1994年   30622篇
  1993年   30342篇
  1992年   26727篇
  1991年   23978篇
  1990年   24181篇
  1989年   23263篇
  1988年   21906篇
  1987年   20008篇
  1986年   19528篇
  1985年   22804篇
  1984年   22706篇
  1983年   20716篇
  1982年   19529篇
  1981年   19670篇
  1980年   18303篇
  1979年   18817篇
  1978年   17961篇
  1977年   18301篇
  1976年   20236篇
  1975年   16205篇
  1974年   15706篇
  1973年   15770篇
  1972年   13263篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
Field surveys of a series of conjugated diunsaturated straight-chain primary alcohols, acetates, and aldehydes (dienes), including the 3,5-dode-cadienyl, 8,10-dodecadienyl, 3,5-tetradecadienyl, 8,10-tetradecadienyl, 9,11-tetradecadienyl, and 10,12-tetradecadienyl primary alcohols, acetates, and most aldehydes, and the related monounsaturated straight-chain primary alcohols, acetates, and aldehydes (monoenes), including the 3-dodecadienyl alcohol and acetates, attracted the following species from the title families. Diene attractants have been demonstrated for at least onePhyllonorycter sp.,Chionodes lugubrella (Fabr.),Leptostales ferruminaria (Zell.),Drepana bilineata (Pack.),Pyrausta fodinalis (Led.),Notocelia purpurissatana Heinr.,Phaneta alterana Heinr. Monoene attractants were demonstrated forHedya separatana (Kft.),Cydia fletcherana (Kft.),Barbara mappana Free.,Ancylis burgessiana (Zell.),Ancylis nubeculana Clem.,Evippe prunifoliella Cham.,Phlyctaenia coronata tertialis (Gn.), aChionodes sp., a Gelechiidae sp., and an unidentifiedPhyllonorycter sp. Replicated field experiments showed attraction-inhibition relationships for most species. Electroantennagram data are presented forLeptostales ferruminaria andDrepana bilineata.  相似文献   
982.
Summary Starting with Z-2, 3-diamino-2-butenedinitrile as diamine component the synthesis of the low molecular N,N,O,O-chelate 3.Co and its ligand 3 is optimized. An easy synthesis of the chelate 8.Co covalently bound on macroreticular resins is presented. The chelates 8.Co are the most active heterogenous catalysts for the valence isomerization of quadricyclane to norbornadiene today.  相似文献   
983.
For the past three decades, IS managers have been faced with the tasks of honing their craft, improving productivity, and serving as the keepers of information technology for the corporation. For the most part, they have done a commendable job. However, the rules of the game are changing. Old solutions are no longer extensible to current problems, and today's problems are unlike any faced in the past. This article takes a fresh look at what the top priorities for IS managers should be in the coming years.  相似文献   
984.
The survey focuses on algebraic-grammatical models of parallel processes, representation of knowledge about classes of algorithms in terms of a variety of production systems (structured design grammars), and program generation tools.Translated from Kibernetika i Sistemnyi Analiz, No. 5, pp. 5–13, September–October, 1991.  相似文献   
985.
An efficient algorithm to remove redundant dependences in simple loops with constant dependences is presented. Dependences constrain the parallel execution of programs and are typically enforced by synchronization instructions. The synchronization instructions represent a significant part of the overhead in the parallel execution of a program. Some program dependences are redundant because they are covered by other dependences. It is shown that unlike with single loops, in the case of nested loops, a particular dependence may be redundant at some iterations but not redundant at others, so that the redundancy of a dependence may not be uniform over the entire iteration space. A sufficient condition for the uniformity of redundancy in a doubly nested loop is developed  相似文献   
986.
Translated from Atomnaya Énergiya, Vol. 66, No. 6, pp. 423–424, June, 1989.  相似文献   
987.
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989.  相似文献   
988.
989.
Geomechanical aspects of the storage of radioactive waste in salt formations have been studied extensively using finite element methods over the last 20 years. In consequence a range of computer programs and associated modelling techniques have been assembled. The paper is based on a benchmark exercise to compare the predictive abilities of a number of these programs and highlights the difficulties of making reliable a-priori estimates of long term behaviour.  相似文献   
990.
Intensive fertilizer use has led to nitrate contamination of groundwater in many areas. This article examines the possibility of removing nitrates through the construction of artificial wetlands. A pilot study conducted in Denmark has found that the method is effective and economical, at least for small waterworks, though further treatment is necessary before an acceptable microbiological water quality is attained.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号